SQL> create table users(
  2  id number(10) primary key,
  3  name varchar2(50),
  4  password varchar2(50))
  5  ;

Table created

SQL> create sequence user_id increment by 1 start with 1 minvalue 1 maxvalue 999999999 cache 10;
Sequence created

SQL> insert into users values(user_id.nextval,'admin','123');
1 row inserted

SQL> commit;
Commit complete